CVE-2026-118173
MISP Guard Incomplete Tag Validation Allows Non-Allowed Taxonomy Tags to Bypass Feed Policy Enforcement
Description
MISP Guard, a proxy that enforces security policies on MISP feed data, contained an incomplete validation check for required taxonomy tags. When a feed event or its attributes carried tags belonging to a required taxonomy (for example, TLP), the guard only verified that at least one tag of that taxonomy matched the configured allowed list. It did not verify that every tag of the required taxonomy present on the event or attribute was in the allowed list. As a result, an event or attribute could simultaneously carry an allowed tag (e.g., tlp:clear) and a non-allowed tag (e.g., tlp:red or tlp:amber) and still pass the guard's policy check. This allowed data marked with a higher classification or sensitivity level to be distributed through feeds configured to only distribute lower-classification data, effectively bypassing the intended data-handling restrictions. The vulnerability affected both event-level and attribute-level tag validation, including attributes nested within objects and shadow attributes. An attacker with the ability to author or modify MISP events in a feed source could include non-allowed taxonomy tags alongside allowed ones to exfiltrate more sensitive data to feed consumers than the guard policy intended to permit.
INFO
Published Date :
Oct. 27, 2026, 7:17 p.m.
Last Modified :
Oct. 27, 2026, 7:17 p.m.
Remotely Exploit :
Yes !
Source :
5a6e4751-2f3f-4070-9419-94fb35b644e8
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 5a6e4751-2f3f-4070-9419-94fb35b644e8 | |||||
| CVSS 4.0 | MEDIUM | 5a6e4751-2f3f-4070-9419-94fb35b644e8 | ||||
| CVSS 4.0 | MEDIUM | 5a6e4751-2f3f-4070-9419-94fb35b644e8 |
Solution
- Implement strict validation for all taxonomy tags.
- Ensure every tag matches the configured allowed list.
- Apply the vendor-provided security update.
- Re-evaluate feed data policies for accuracy.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-118173.
| URL | Resource |
|---|---|
| https://github.com/MISP/misp-guard/commit/6127d94c350e4dfe31fd4426ba26f51294ed3867 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-118173 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-118173
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-118173 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-118173 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by 5a6e4751-2f3f-4070-9419-94fb35b644e8
Oct. 27, 2026
Action Type Old Value New Value Added Description MISP Guard, a proxy that enforces security policies on MISP feed data, contained an incomplete validation check for required taxonomy tags. When a feed event or its attributes carried tags belonging to a required taxonomy (for example, TLP), the guard only verified that at least one tag of that taxonomy matched the configured allowed list. It did not verify that every tag of the required taxonomy present on the event or attribute was in the allowed list. As a result, an event or attribute could simultaneously carry an allowed tag (e.g., tlp:clear) and a non-allowed tag (e.g., tlp:red or tlp:amber) and still pass the guard's policy check. This allowed data marked with a higher classification or sensitivity level to be distributed through feeds configured to only distribute lower-classification data, effectively bypassing the intended data-handling restrictions. The vulnerability affected both event-level and attribute-level tag validation, including attributes nested within objects and shadow attributes. An attacker with the ability to author or modify MISP events in a feed source could include non-allowed taxonomy tags alongside allowed ones to exfiltrate more sensitive data to feed consumers than the guard policy intended to permit. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-20 Added CWE CWE-285 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/118xxx/CVE-2026-118173.json">CVE-2026-118173</a> Added Reference https://github.com/MISP/misp-guard/commit/6127d94c350e4dfe31fd4426ba26f51294ed3867 Added SSVC {'role': 'Supplier', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-10-27T18:09:46Z'}